Time-of-flight (TOF) mass spectrometers can suffer from mass accuracy drifting primarily due to thermal expansion/contraction of a flight tube of the mass spectrometer. To achieve improved mass accuracy, time-of-flight mass spectrometers often employ a regular calibration routine in which a calibrant substance of known mass (“lock mass”) is introduced into the mass spectrometer at regular intervals, typically as often as every 30 seconds. In some known mass spectrometers, a mechanism (e.g., a mechanical baffle controlled by a stepper motor) is used to select effluent from either a calibrant electrospray stream or an analyte electrospray stream. These mechanisms generally operate by physically blocking effluent from one of the electrospray streams while effluent from the other electrospray stream is allowed to enter an inlet orifice of the mass spectrometer. Such mechanisms can be cumbersome and can introduce multiple points of mechanical failure. Such mechanisms can also inhibit optimal positioning of an analyte sprayer, which can result in reduced sensitivity. While it may be possible to simply turn off an actuating voltage to either of these spray sources while the other is spraying, the flow to these sprayers would likely continue resulting in a buildup of solution at the associated sprayer, which, in turn, could cause unstable spraying once the spay voltage is reapplied.